Pipe Bending Machine

ABSTRACT

A pipe bending machine has a beam mounted in see-saw pivotal relation on a fulcrum and spaced apart cradles support the pipe. An actuator initially drives the second cradle and the beam apart to pivot the pipe about the first cradle until the pipe is in contact with the die and thereafter drives the beam away from the second cradle to bend the pipe against the die. The mechanical advantage of the levered operation requires only a single actuator motion to bend the pipe. An external mandrel allows the pipe to be incrementally fed through the bending machine and secures the pipe against cross-sectional distortion during the bending process.

CROSS-REFERENCE TO PENDING APPLICATION

This application claims priority U.S. Provisional Application No. 61/328,560, filed Apr. 27, 2010.

BACKGROUND OF THE INVENTION

This invention relates generally to pipe bending and more particularly concerns both the efficiency of pipe bending equipment and the quality of the bends which are created.

Throughout the world each year, thousands of miles of large diameter pipe are assembled and laid underground for transporting oil, natural gas, refined petroleum products, and other fluids. One prior art bending machine has a frame; a caterpillar assembly or other system for moving the portable bending machine from location to location; a bending die which is mounted in fixed position in an upper portion of the frame; a stiffback trough and a pin-up shoe. To begin the pipe bending operation, a segment of pipe is inserted into the pipe bending machine from the rear end thereof such that the pipe segment extends over the pin-up shoe and onto the stiffback trough. Rollers are provided at the forward end of the stiffback trough to facilitate the insertion, relocation, and removal of the pipe segment. An axial positioning mechanism is used to move the pipe segment along the stiffback trough until the portion of the pipe wherein the bend is to be made is properly positioned beneath the bending die. The bending die has a curved bending surface which contacts the top of the pipe and is shaped to impart a desired bend radius to the pipe segment during the bending operation. The stiffback trough is connected to the frame by a pair of outboard hydraulic bending cylinders which are secured between the front portion of the frame and the front portion of the stiffback trough. In addition, four inboard hydraulic cylinders are connected between the upper portion of the frame and the rear portion of the stiffback trough. The pin-up shoe is connected to the rear portion of the frame for supporting the rear portion of the pipe segment during the bending operation. The vertical position of the pin-up shoe can be adjusted by sliding a pin-up wedge beneath the shoe using a hydraulic pin-up cylinder. After the pipe segment has been inserted and axially positioned in the bending machine, the stiffback trough is raised vertically to bring the upper surface of the pipe segment into contact with the bending die. This procedure, referred to as “leveling,” is accomplished using the outboard and inboard bending cylinders. Next, the pin-up cylinder is extended to move the pin-up wedge against the pin-up shoe so that the shoe contacts the lower surface of the pipe segment. With the pipe shoe in contacting position, the outboard cylinder is then operated to provide a lifting force to the outer end of the stiffback trough such that the stiffback trough imparts a bending moment to the pipe segment sufficient to cause the pipe segment to bend upwardly against the curved bending surface of the bending die. At the same time that the outboard cylinders are operated to apply the necessary bending moment to the pipe segment. The in board cylinders of the prior art machine must also be operated to raise the rearward end of the stiffback trough in order to clamp the pipe segment against the bending die.

Heretofore, when bending a pipe segment using a bending machine of the type illustrated in FIGS. 1 and 2, it has been necessary to fill the pipe with a filling material or to insert a bending mandrel into the pipe to prevent the pipe wall from wrinkling, buckling, or egging during the bending operation. In recent years, the potential for distortion, wrinkling, buckling, or egging has increased significantly as the industry has moved toward the use of higher tensile strength materials to form more economical pipes having significantly reduced wall thicknesses. Because of significant disadvantages and limitations involved in the use of filling materials, the insertion of a bending mandrel into the pipe within the area of the bend has heretofore been the preferred method for protecting the pipe during bending operations. An internal bending mandrel will operate to apply a supporting force to the upper interior portion and the lower interior portion of the pipe wall during the bending operation. Thus, the mandrel applies upward and downward interior supporting forces which are substantially directed, in a general sense, in opposite directions along the vertical bending plane. The upper interior portion of the pipe wall acted upon by the internal bending mandrel will typically extend over an arc of the interior pipe wall. The lower interior portion of the pipe wall acted upon by the internal bending mandrel will typically extend over an arc of the interior wall. The bending mandrel will typically include a set of wheels or rollers which allow the mandrel to be driven or pulled into, and properly positioned within, the interior of the pipe. Also, the mandrel is articulated or is otherwise configured such that, at the same time that the bending mandrel applies upward and downward interior forces to the pipe during the bending operation, the mandrel remains flexible enough in the longitudinal direction to allow the mandrel to bend with the pipe. However, even though the mandrel has a sufficient degree of longitudinal flexibility to accommodate the bending of the pipe, the fact that the internal bending mandrel must apply significant retaining force during the bending operation in generally the same vertical plane as the bending movement is disadvantageous. Unfortunately, the use of an internal bending mandrel significantly increases the time, cost, and complexity of the bending operation. Bending mandrels are complex and expensive and typically require the use of a separate operating system. Significant time and effort are required to insert, position, operate, relocate, and remove the bending mandrel during the bending operation. In addition, the specific mandrel selected for any given application must be sized and suitable for a particular range of bend radii and must match the diameter, wall thickness, and strength of the pipe. Further, even when using an internal mandrel, it is often difficult to keep the cross section of the pipe entirely round during the bending operation, which, in addition to other problems, can be detrimental to corrosion coatings which have likely been applied to pipe. Also, even with the use of an internal bending mandrel, distortion, flattening, and buckling can sometimes still occur because the internal mandrel is simply not adequate to support the bend. Another significant disadvantage of using an internal bending mandrel is that the stiffback trough of the bending machine must be an elongate structure of sufficient length that (a) the outboard bending cylinders connected to the forward end of the stiffback trough are spaced a sufficient distance forward of the bending die to provide the necessary bending moment force without creating an unreasonable power demand and (b) the rearward end of the stiffback trough extends at least a sufficient distance beneath the bending die such that the rearward end of the stiffback trough will be positioned beyond the applied bending arc.

Unfortunately, the need to extend the stiffback trough beneath the bending die also necessitates that the inboard leveling cylinders be positioned behind the pipe bending point. Thus, the inboard cylinders in effect create a competing bending moment which further increases the required size and output of the outboard cylinders and also increases the strength and weight requirements of the machine frame and other components.

Also, when using a prior art internal bending mandrel, it has been necessary that (a) the stiffback trough have an upwardly curved interior surface having a size and shape corresponding the bottom half of the pipe and (b) the bending die have a downwardly curved interior which similarly corresponds to the size and shape of the upper half of the pipe. Thus, together, the stiffback trough and the bending die substantially surround the pipe during the bending operation except for a small longitudinal gap between the two on each side of the pipe near the pipe's horizontal center plane. The use of stiffback trough and bending die structures of this type which substantially surround the pipe, as well as the need to apply a leveling and clamping force to the stiffback trough at location behind the bend point, have inherently been required heretofore when using an internal bending mandrel to further ensure that no distortion, wrinkling, buckling, and egging occurs.

Thus, a need exists for a more economical, efficient, and reliable system and method for bending pipe. Such system will preferably (a) eliminate the need for inserting a bending mandrel into the interior of the pipe to protect the pipe from distortion, wrinkling, buckling, or egging during the bending operation, (b) eliminate the need for an inboard leveling and clamping cylinder arrangement which exerts an undesirable competing bending moment force against the stiffback trough, and (c) reduce the strength and weight requirements of the bending machine frame and other components, (d) significantly reduce the complexity and cost of the bending system and process, (e) provide increased speed, efficiency, and precision, (f) increase the life span of the equipment and system, (g) provide reconfigured load points which allow more efficient use of hydraulic energy, (h) provide an increased mechanical advantage to existing hydraulic components without increasing the power demand, and (i) provide better stress distribution to the machine frame.

Pipe bending requires application to the pipe of forces of various magnitudes and in various directions. The force magnitudes required generally increase in relation to the diameters and thicknesses of the pipes being bent. The strength of the supporting structure and the number, type and size of actuating components that are presently deemed necessary to manipulate and bend the pipe result in the design of heavy, immobile, slow-operating, expensive machines. in To handle in multiple directions and involving a multitude of force exerting actuators. In bending steel pipe, In the use of known pipe bending equipment, as a pipe is loaded into the bending machine, the pipe simultaneously internally receives a mandrel. which is aligned in the machine on the path of pipe insertion. The mandrel is intended to prevent the occurrence of out-of-round deviation, or buckling, of the pipe as bending forces are applied to the pipe during the bending process.

It is, therefore, among the objects of this invention to provide a pipe bending machine and method which limit the likelihood of distortion, wrinkling, buckling, and egging of the pipe, eliminate the need for an internal bending mandrel, simplify the bending operation, provide improved bending protection, efficiency, speed, and precision, increase the life span of the bending equipment, eliminate the application of wasteful competing bending moments, provide better stress distribution on the bending machine frame, reduced power demand, apply energy more efficiently, increase mechanical advantage and reduce the strength and weight requirements of the machine frame and other components.

SUMMARY OF THE INVENTION

In accordance with the invention, a pipe bending machine is provided which reduces the number and size of actuators and supporting structure needed to bend a pipe and/or which retains the shape of the pipe by acting against and holding the exterior of the pipe during the bending operation.

To retain the shape of the pipe, a mandrel is provided which has a plurality of pairs of members, each pair having an inner contour shaped to mate against the exterior wall of the pipe to substantially maintain the cross-sectional shape of the pipe during bending. Each pair has an inner contour shaped to urge the members to mate against the exterior wall of the pipe as the pipe is impelled against the urging inner contour. Preferably, each pair is independently pivotally mounted so as to be at rest in response to gravity in a sufficiently open condition to receive a pipe and to close on and concentrically mate against the exterior wall of the pipe in response to the pipe imposing force against the internal contour.

To reduce the number and size of supporting actuators and structure, the machine for bending the has a beam mounted in see-saw pivotal relation on a fulcrum. First and second spaced apart cradles are aligned to support the pipe. The first cradle is mounted on the beam on one side of the fulcrum and the second cradle is mounted on an actuator mounted on the beam on an opposite side of the fulcrum. A die is positioned between the cradles. The actuator initially drives the second cradle and the beam apart to pivot the pipe about the first cradle until the pipe is in contact with the die and thereafter drives the second cradle away from the beam to bend the pipe against the die. Thus, a single actuator motion is all that is required to bend the pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 is a free body diagram illustrating the operation of bending leverage components of the pipe bending machine in the initial pipe to die contact position;

FIG. 2 is a free body diagram illustrating the operation of bending leverage components of the pipe bending machine during bending of the pipe;

FIG. 3 is a free body diagram illustrating a first embodiment of the actuator of FIGS. 1 and 2;

FIG. 4 is a free body diagram illustrating a second embodiment of the actuator of FIGS. 1 and 2;

FIG. 5 is a top/side perspective view illustrating the operation of the external mandrel of the pipe bending machine;

FIG. 6 is an end elevation view looking downstream at the external mandrel of FIG. 5 in its open at rest condition;

FIG. 7 is an end elevation view looking downstream at the external mandrel of FIG. 5 in its pipe gripped condition;

FIG. 8 is a side elevation view of a preferred embodiment of the pipe bending machine in a pipe loaded condition with a side frame of the machine removed;

FIG. 9 is a side elevation view of a preferred embodiment of the pipe bending machine with the pipe in a bent condition with a side frame of the machine removed;

FIG. 10 is a bottom/side perspective view looking downstream of a preferred embodiment of the radial control arm of the pipe bending machine of FIGS. 7 and 8;

FIG. 11 is a side perspective view looking downstream at a preferred embodiment of the external mandrel of the pipe bending machine of FIGS. 8 and 9 in its pipe gripped condition;

FIG. 12 is a top plan view of the external mandrel of FIG. 11;

FIG. 13 is a bottom plan view of the external mandrel of FIG. 11;

FIG. 14 is a front/bottom perspective view looking downstream at a preferred embodiment of the external mandrel of the pipe bending machine of FIGS. 8 and 9 in its pipe gripped condition with the pipe removed;

FIG. 15 is a top/side perspective view looking downstream at the upstream bending portion of the external mandrel of the pipe bending machine of FIGS. 8 and 9 in its pipe gripped condition before bending of the pipe (not shown);

FIG. 16 is a top/side perspective view looking downstream at the upstream bending portion of the external mandrel of the pipe bending machine of FIGS. 8 and 9 in its pipe gripped condition after bending of the pipe (not shown);

FIG. 17 is an end elevation view looking upstream at the external mandrel of the pipe bending machine of FIGS. 8 and 9 in its open at rest condition;

FIG. 18 is an end elevation view looking upstream at the external mandrel of the pipe bending machine of FIGS. 8 and 9 in its pipe (not shown) gripped condition;

FIGS. 19A, 19B and 19C perspective end views illustrating the progression of the mandrel of the pipe bending machine of FIGS. 8 and 9 through pipe loaded, pipe gripped and pipe bent conditions, respectively; and

FIGS. 20A, 20B and 20C are cross-sectional views taken along the lines 20A-20A, 20B-20B and 20C-20C of FIGS. 19A, 19B and 19C, respectively.

While the invention will be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments or to the details of the construction or arrangement of parts illustrated in the accompanying drawings.

DETAILED DESCRIPTION

The Lever

Turning first to FIG. 1, the lever assembly 10 of the machine for bending pipe P includes a beam 11 mounted in see-saw pivotal relation on a fulcrum 13. Downstream and upstream spaced apart cradles 21 and 25 are aligned to support the pipe P as it is intervally moved in the downstream direction 19 along the lever assembly 10. The downstream cradle 21 is mounted on the beam 11 on one side of the fulcrum 13. The upstream cradle 25 is mounted on an actuator 27 which is mounted on the beam 11 on an opposite side of the fulcrum 13 as the downstream cradle 21. A die 20 is positioned between the cradles 21 and 25, as shown approximately above and upstream of the fulcrum 13. The actuator 27 initially drives the upstream cradle 25 and the beam 11 apart to pivot the pipe P about the downstream cradle 21 until the pipe P is in contact with the die 20. The force exerted by the actuator 27 is selected so that, until the pipe P contacts the die 20, the force applied on the pipe P by the actuator 27 at the upstream cradle 25 is insufficient to bend the pipe P. However, because of the leverage created at the fulcrum 13 after the pipe P contacts the die 20, the force exerted on the pipe P at the upstream cradle 21 is sufficient to bend the pipe P against the die 20.

As seen in FIG. 1, the initial point of contact 29 between the pipe P and the die 20 is the point at which the bend in the pipe P will begin. Consider a vertical reference plane 31 perpendicular to another vertical plane defined by the longitudinal axis of the pipe P and passing through the nadir 33 of the die 20. As seen, the initial contact point 29 of the pipe P with the die 20 is on the upstream portion of the pipe P. The amount of force applied to the upstream portion of the pipe P depends on the mechanical advantage provided by the location of the fulcrum 13 between the clamps 21 and 25 on the beam 11, which is fixed, and the location of the bending point of the pipe P between the clamps 21 and 25, which varies as the pipe P bends. Since the fulcrum 13 and the cradles 21 and 25 are fixed on the beam 11, changing the location of the fulcrum 13 in relation to the reference plane 31 will also change the location of the downstream cradle 21 in relation to the reference plane 31. Since the downstream cradle 21 is the pivot point for rotation of the pipe P into contact with the die 20, the angular relationship of the pipe P to the die 20 would change and, therefore, the point of initial contact 29 with the die 20 would also change. Looking at FIG. 2, as bending continues the fulcrum 13 is fixed in relation to the reference plane 31 but the point of contact of the pipe P with the die 20 shifts toward the upstream end of the pipe P. Thus, the amount of force applied to the bend portion of the pipe P varies as the point of contact 29 changes during bending. The location of the fulcrum 13 in relation to the reference plane 31 is a significant factor in the amount of force applied in bending the pipe P. As the distance 35 from the center of the downstream cradle 21 to the contact point decreases, the distance 37 from the center of the upstream cradle 25 to the contact point decreases, applying decreasing force to the upstream portion of the pipe P. The downstream reaction force is determined by the ratio R=Y/X. If the downstream reaction force is too high, for example if R>2.5, the pipe P may experience undesired deformation or ovality. It has been empirically found to be ideal, though not necessary, to maintain a range of 1.5<R<2 with the fulcrum 13 located approximately 6″ aft, or toward the upstream cradle 25, of the reference plane 31.

Looking at FIG. 3, the actuator 27 of FIGS. 1 and 2 may be an hydraulic cylinder 41 connected between the beam 11 and the upstream cradle 25. Looking at FIG. 4, the actuator 27 of FIGS. 1 and 2 may be a screw-drive 43, as shown driven by an electric motor 45. The actuator 27 of FIGS. 1 and 2 may, however, be of any type, whether pneumatically, hydraulically or electrically driven.

The Mandrel

Turning to FIGS. 5-7, the external mandrel 50 of the machine for bending pipe P has a plurality of pairs of members or cleats 67 and 69. Each pair of cleats 67 and 69 has an inner contour shaped to mate against the exterior wall of the pipe P to substantially maintain the cross-sectional shape of the pipe P during bending. Each pair of cleats 67 and 69 also has an inner contour 71 shaped to urge the cleats 67 and 69 to mate against the exterior wall of the pipe P as the pipe P is impelled against the urging inner contour 71. Preferably, each cleat 67 and 69 of a pair is independently mounted on a rod, hub, axle or other type of pivot 57. The downstream portions (not shown in FIGS. 5-7) of the flexible rods 57 are fixed, so that the rods 57 extend upstream in a substantially horizontal and parallel relationship, as is best seen in FIG. 5.

Retainers 53 and spacers 55 are alternately mounted on the outer perimeters of the upstream portions of the rods 57 by sliding inwardly facing notches on their opposite ends onto the rods 57. The cleats 67 and 69 are mounted on the inner perimeters of the rods 57 by sliding outwardly facing notches 75 on their opposite ends onto the rods 57. The inner perimeters of the rods 57 and the outer perimeters of the notches 75 in the cleats 67 and 69 are complementarily arcuate to facilitate pivoting of the cleats 67 and 69 on the rods 57.

As shown, the cleats 67 and 69 have thick lower portions with thinner upper tongue portions 77. The retainers 53 have the same thickness as the tongues 77 and the spacers 55 have a thickness that fills the gap created between the tongues 77 of abutting pairs of cleats 67 and 69. The result is that the retainers 53, which are centered on the pairs of cleats 67 and 69, and the spacers 55, each of which are shared by face-to-face cleats 67 and 69 of sequential pairs, form an assembly which resists twisting and wobbling during the bending process.

Looking at FIG. 6, the cleats 67 and 69 of each pair are spaced apart so that they are free to rotate about their respective rods 57 in response to gravity into an at-rest position in which they create a pair of jaws sufficiently open to enable insertion of the outer diameter of the pipe P upwardly between the cleats 67 and 69. A stop 81, as shown in the form of co-operable lands on the tongues 77 of the cleats 67 and 69 and on their respective retainers 53, limits further rotation of the cleats 67 and 69 beyond their sufficiently open condition.

As seen in FIG. 7, headroom 83 is provided between the tops of the tongues 77 of the cleats 67 and 69 and the bottoms of the retainers 53 so that the retainers 53 cannot obstruct the concentric mating of the pipe P with the internal contours 71 of the cleats 67 and 69. Headroom 85 is also provided between the tops of the lower portions of the cleats 67 and 69 (at the bottoms of the tongues 77) and the bottoms of the spacers 55.

Continuing to look at FIG. 7, a pair of cleats 67 and 69 will be caused to close on, and their internal contour 71 caused to concentrically mate against, the exterior wall of the pipe P in response to the pipe P imposing upward force against the upper portion of their internal contour 71. This occurs during the initial application of non-bending force to the pipe P, as described above in relation to FIGS. 1 and 2. Once a pair of cleats 67 and 69 has come into concentric abutment with the outer surface of the pipe P, the continued application of bending force to the pipe P will cause the rods 57 to flex upwardly, allowing that pair of cleats 67 and 69 and the curvature of the pipe P contained therein to conform to the curvature of the die 20, as seen in FIGS. 1 and 2. Each pair of cleats 67 and 69 will be sequentially actuated in their upstream order to mate against the pipe P as the pipe P is impelled against the internal contours 71 of the pair. This sequential mating continues until the section of the pipe P contained along the flexing length of the rods 57 has been bent to conform to the curvature of the die 20. Once bent, cessation of application of the bending force allows the bent pipe P, the pairs of cleats 67 and 69 and the flexed upstream portion of the rods 57 to release to gravity. The pipe P can then be advanced downstream in the mandrel 50 and the process repeated until the desired length of pipe P has been bent.

Returning to FIG. 7, the geometry of the retainers 53 is significant in minimizing and/or controlling the amount of variation in ovality of the bent pipe P. As noted above, the head clearance 83 of the retainers 53 affords an increased range of upward motion of the retainers 53 that enables the retainers 53 to act as squeeze levers or cams against the pipe P. Therefore, the strength of the squeeze can be controlled to some extent by adjusting the amount of head clearance 83. Also, consider the horizontal distance from the pivot surface of a rod 57 to the uppermost point of its corresponding member contour 73 as the arm of a retainer R_(arm) and the vertical distance from the pivot surface of the rod 57 to the horizontal diameter of the curvature of the member contour 71 as the leg of the retainer R_(leg). The arm/leg ratio R=R_(arm)/R_(leg) determines the strength of the squeeze applied to the pipe P during the bending operation. If R<1, more pipe cross-section deformation will occur than if R>1. Increased arm length R_(arm) increases deformation and increased leg length R_(leg) decreases deformation. Empirically, R=1.3 appears to produce the best results.

The Bending Machine

A preferred embodiment of a bending machine 100 incorporating the principles of the lever assembly 10 and mandrel 50 above described is illustrated in FIGS. 8-9. The lever assembly 110 of the machine 100 has a beam 111 mounted in see-saw pivotal relation on a fulcrum 113. The fulcrum 113 is mounted on a base frame 115 carried on a pair of non-motorized track assemblies 117 which are aligned on the machine 100 in parallel with the longitudinal axis of the pipe P. The track assemblies 17 could be motorized.

Pipe P feeds through the bending machine 100 in a downstream direction 119. A first pipe cradle 121 is mounted near the downstream end of the beam 111 on an axle or other pivot member 123 which allows the downstream cradle 121 to rotate so that the pipe P will remain fully seated in the cradle 121 throughout the bending process. A second cradle 125 is mounted on a scissor 127 with upper and lower arms 129 and 131 extending from intermediate joints 133. The scissor 127 is driven by a screw drive 135 powered by a motor 137. The upstream cradle 125 is connected to the scissor upper arms 129 by an axle or other pivot member 139 which allows the upstream cradle 125 to rotate so that the pipe P will also be fully seated in the upstream cradle 125 throughout the bending process. The bottom joint 141 of the scissor 127 is mounted on the beam 111. As shown, the bottom joint 141 preferably consists of two spaced apart joints 141 so as to provide greater control and efficiency in the operation of the scissor 127. The beam fulcrum 113 divides the beam 111 into downstream and upstream portions, as shown in such a proportion as to apply an approximately 2:1 mechanical advantage from the screw drive 135 to the pipe P at the downstream cradle 121 in comparison to the upstream cradle 125. The upstream end of the beam 111 has a supporting frame assembly 143 mounted to the beam 111. The frame assembly 143 supports the beam 111 on the ground during the bending operation. The beam 111 also supports downstream and upstream rollers 145 and 147;respectively, to facilitate loading Of the pipe P into the machine 100 and onto the cradles 121 and 125.

A radial control arm 151 is connected at its downstream end on an axle or other pivot member 153 to the beam 111 at a point upstream of the fulcrum 113 and below the downstream roller 145. As seen in FIG. 8, the radial control arm 151 is connected at its upstream end on an axle or pivot member 155 mounted on the bottom of the upstream cradle 125. Looking at FIG. 10, the preferred embodiment of the radial control arm 151 has telescoping channels 157 and 159. The downstream end of the main inner channel 157 is adapted, or by a sleeve 161, to be mounted on the downstream pivot member 153 and the upstream end of the shorter channel 159 is adapted, or by the fork 163 and sleeves 165, to be mounted on the upstream pivot member 155 with the fork 163 straddling the upstream cradle 125. The web of the main channel 157 has three elongated slots 167 in its upstream end exposing the web of the shorter channel 159. A center plate 169 affixed to the web of the shorter channel 159 extends through the center slot 167 into the main channel 157. Upstream and downstream end plates 171 and 173 are also fixed to the web of the shorter channel 159 and extend through the upstream and downstream slots 167 into the main channel 157. A pair of parallel shafts 175 extends across the center and end plates 169, 171 and 173. Bearings 177 which slide on the shafts 175 are mounted on intermediate plates 179 which are fixed to the web of the main channel 157 with tension springs 181 on the shafts 175 between the center and intermediate plates 169 and 179. Clamps 183 secure the shafts 175 against the center and end plates 169, 171 and 173 to hold the radial control arm assembly 151 together. The downstream roller 145 is preferably mounted on the downstream end of the assembly 151 above its downstream pivot sleeve 161 and a ramp 185 is mounted on the main channel 157 immediately upstream of the roller 145 to assure that the pipe P is guided onto the roller 145 as the pipe P is loaded into the machine 100.

Returning to FIGS. 8 and 9, the bending machine 100 also includes a die assembly 200 with a preferred embodiment of an external mandrel 250 according to the principles discussed in relation to FIGS. 5-7. As shown, the die assembly 200 is mounted between the outer side plates 211 of a die support frame and is longitudinally positioned between the cradles 121 and 125 approximately above and upstream of the fulcrum 113, as earlier explained.

The preferred embodiment of the die assembly 200 is illustrated in greater detail in FIGS. 11-18, 19A-C and 20A-C. As seen in FIGS. 11-14, the die 200 has side plates 211 and a center plate 213 spaced by sleeves 215 and held together by tie rods 217 and bolts 219. As best seen in FIGS. 15 and 16, grooves 221 in the bottom edges of the upstream portions of the side and center plates 211 and 213 of the die 200 receive the upwardly extending tongues 223 of die radius members 225. The curvature of the lower faces of the die radius members 225 determines the bend of the pipe P and they are removably secured to their respective side and center plates 211 and 213 by bolts 227 extending through the tongues 223, so that the bending radius of the machine 100 can be changed by replacing the die radius members 225. Returning to FIGS. 11-14, machine mounting shafts 229 extend transversely across the die assembly 200 and rest in seats 231 on top of the plates 211 and 213. Clamps 233 extending across the mounting shafts 229 and connected to the outer plates 211 by bolts 235 secure the mounting shafts 229 in their respective seats. Eye bolts 237 extending above the clamps 233 facilitate moving and manipulation of the die assembly 200.

A preferred embodiment of the external mandrel 250 associated with the die 200 is illustrated in greater detail in FIGS. 11-18, 19A-C and 20A-C. The upstream portion of the mandrel 250 may be envisioned as a plurality of vertebra 251 formed by retainers 253 alternately mounted with spacers 255 on rods 257 which are the spine 259 of the mandrel 250. Each upstream vertebra 251 consists of one retainer 253 and the abutting portions of its adjacent spacers 255, each spacer 255 being shared by two retainers 253. As noted above, the structure of the die assembly 200 coupled with the interfacing of the retainers 253 and spacers 255 contribute to the prevention of any twisting or wobbling of the mandrel 250 during the bending process.

Looking at FIGS. 11-16, the downstream ends of the rods 257 are secured in fixed relationship to downward extensions 261 of the downstream portion of the side plates 211. As best seen in FIGS. 15 and 16, the cantilevered or upstream ends of the rods 257 are free to deflect upwardly in response to application of bending force to the pipe P, causing the spine 259 of the mandrel 250 and its vertebrae 251 to elastically conform to the curvature of the die radius members 225. Looking at FIGS. 11 and 14, the upstream portion of the spine 259 is prevented from deflecting below horizontal by retaining members 263 mounted on the outer surface of the side plates 211 which engage, when the rods 257 drop to horizontal, with stubs 265 fixed to the upstream ends of the rods 257.

Along the upstream portion of the spine 259, each vertebra 251 has an associated pair of jaws 267 and 269, one jaw 267 of each pair being mounted on one of the rods 257 and the other jaw 269 of each pair being mounted on the other of the rods 257. The jaws 267 and 269 are independently pivotally mounted so that each pair of jaws 267 and 269 is freely at rest in response to gravity in a sufficiently open condition to receive the pipe P. Each pair of jaws 267 and 269 has an internal contour 271 or 273 shaped at least in part to cause the pair of jaws 267 and 269 to close on and concentrically mate against an exterior wall of the pipe P in response to the pipe P imposing force against the internal contour 271 or 273 so that the mandrel 250 substantially maintains the cross-sectional shape of the pipe P during bending. As best seen in FIG. 13, it is preferred that the jaws 267 and 269 contact the pipe P extends to slightly below the horizontal diameter of the pipe P.

Looking at FIGS. 17 and 18, in the downstream portion of the mandrel 250, the spine 259 does not flex. Therefore, the downstream jaws 267 and 269 are mounted on the rods 257 without the retainers 253 or spacers 255. To control the rotation of the downstream jaws 267 and 269, a pair of longitudinal stop plates 275 are mounted on the sleeve 215 of the die 200 to provide co-operating lands 277 to engage the lands of the jaws 267 and 269. Gussets 279 welded to the side plates 211 of the die 200 assist in minimizing any deflection of the spine 259 components of the mandrel 250.

Operation

As seen in FIGS. 8 and 9, the fulcrum 113 is positioned aft or downstream of the initial contact point of the pipe P with die 200 which occurs at the downstream flex point of the rods 157.

In the operation of the machine 100, after the pipe P has been loaded horizontally downstream onto the rollers 145 and 147 of the lever assembly 110 of the machine 100, the screw drive 135 initially causes the scissor 127 to expand vertically, causing the distance between the upstream cradle 125 and the beam 111 to increase and thereby elevate the upstream cradle 125 to pick up the pipe P. At the same time, the downstream cradle 121, which is mounted on the downstream side of the fulcrum 113, is elevated by the beam 111 to pick up the pipe P. As the screw drive 135 continues its vertical expansion, the pipe P continues to be elevated by both cradles 121 and 125 while the pipe P pivots on the downstream cradle 121, changing its angular relation to the beam 111. Eventually, the pipe P makes contact with the die assembly 200, at which time the pipe P is pinned between the downstream cradle 121 and the downstream portion of the die assembly 200. At this time, the downstream portion of the pipe P has been inserted into and mated with the downstream portion of the external mandrel 250. However, the force exerted by the screw drive 135 on the moving beam 111 was selected to be less than the force required to bend the pipe P. But, as the screw drive 135 continues to drive between the upstream cradle 125 and the beam 111, the beam has been immobilized by the fixed positions of the downstream cradle 121 and the die assembly 200 and can no longer pivot on the fulcrum 113. Therefore, the force of the screw drive 135 multiplied by the mechanical advantage of the lever assembly 110 will be applied to the upstream portion of the pipe P, bending the portion of the pipe P in the upstream portion of the mandrel 250 to be sequentially inserted into and mated with the jaws 267 and 269 of the upstream portion of the external mandrel 250 and then bent into conformance with the die assembly 200. While the mechanical advantage shown is approximately 2:1, other mechanical advantage ratios can be used provided they result in exertion of pipe bending force only after the pipe P has contacted the die assembly 200 and is mated in the downstream jaws 267 and 269 of the external mandrel 250.

Turning to FIGS. 19A, 19B and 19C, the pipe P is intermittently fed longitudinally through the jaws 267 and 269 of the mandrel 250 with the jaws 267 and 269 released to gravity to assume the at-rest “opened” condition. At each incremental advancement of the pipe P, the pipe P is urged against the upper inner contour 273 of the jaws 267 and 269 through which the pipe P extends to cause the jaws 267 and 269 to close on the pipe P. The entire inner contour 273 of the jaws 267 and 269 girths the exterior wall of the pipe P to substantially maintain the cross-sectional shape of the pipe P as it is being bent. As best seen in FIGS. 20A, 20B and 20C, considering the portion of the pipe P which is within the external mandrel 250, as the upstream portion of the pipe P is raised to the pin-up condition, the pipe P sequentially comes into contact with further upstream jaws 267 and 269.

As the bending force is applied to the pipe P, the force applied may tend to urge the upstream cradle 125 to shift on the pipe P. The radial control arm 151 provides counter-acting force on the upstream cradle 125 to offset this tendency. The pipe P is then released by termination of the applied force and the weight of the pipe P assists gravity in causing the jaws 267 and 269 to rotate back to the gravity-maintained at-rest “opened” condition. The pipe P is then advanced for the next incremental distance and the process repeated until the desired length pipe P is bent to the radius established by the die 200.

Thus, it is apparent that there has been provided, in accordance with the invention, an on-board external mandrel that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims. 

1. For use in a machine for bending pipe, a mandrel comprising a plurality of vertebra, each said vertebra having a pair of jaws, each jaw of said pair being independently pivotally mounted whereby said pair of jaws is at rest in response to gravity in a sufficiently open condition to receive a pipe therein, each said pair of jaws having an internal contour shaped at least in part to cause said pair of jaws to close on and mate against an exterior wall of the pipe in response to the pipe imposing force against said internal contour whereby the mandrel substantially maintains a cross-sectional shape of the pipe during bending thereof.
 2. A mandrel according to claim 1, said plurality of vertebra forming a spinal column which, with said vertebrae mated against the pipe in said closed condition, is free to conform to a bending arc of the pipe.
 3. For use in a machine for bending pipe, a mandrel comprising a plurality of vertebra, each said vertebra having a pair of jaws, each jaw of said pair being independently pivotally mounted whereby each said pair of jaws is at rest in response to gravity in a sufficiently open condition to transversely receive a pipe being elevated into said pair of jaws, each said pair of jaws having an upper internal contour shaped to cause said pair of jaws to rotate into a closed condition on the pipe in response to the pipe being elevated against said upper internal contour and to bear against an exterior wall of the pipe in said closed condition to substantially maintain a cross-sectional shape of the pipe during bending thereof.
 4. A mandrel according to claim 3, said plurality of vertebra forming a spinal column which, with said vertebrae bearing against the pipe in said closed condition, is free to conform to a bending arc of the pipe.
 5. For use in bending pipe, a machine comprising: a frame; a plurality of vertebra mounted on said frame to form a spinal column which is free to conform to a bending arc of the pipe; and a lower trough movably mounted in said frame to bend the pipe against said spinal column; each said vertebra having a pair of jaws, each jaw of said pair being independently pivotally mounted whereby said pair of jaws is at rest in response to gravity in a sufficiently open condition to transversely receive the pipe as the pipe is elevated into said pair of jaws, each said pair of jaws having an upper internal contour shaped to cause said pair of jaws to rotate into a closed condition on the pipe in response to the pipe being elevated against said upper internal contour and each said pair of jaws having an internal contour shaped to bear against an exterior wall of the pipe in said closed condition to substantially maintain a cross-sectional shape of the pipe during bending thereof.
 6. For use in bending pipe, a mandrel comprising: a plurality of pairs of members; each said pair having an inner contour shaped to mate against an exterior wall of the pipe to substantially maintain a cross-sectional shape of the pipe during bending thereof; and each said pair having an inner contour shaped to urge said members to mate against the exterior wall of the pipe as the pipe is impelled against said urging inner contour.
 7. A mandrel according to claim 6, said members of each said pair having their respective said mating surfaces diametrically opposed when mated against the pipe.
 8. For use in bending pipe, a machine comprising: a frame; an upper die mounted in said frame; a lower trough movably mounted in said frame to bend the pipe against a surface of said die; a plurality of pairs of members mounted on said frame to freely conform to a bending arc of the pipe, each said pair having an inner contour shaped to mate against an exterior wall of the pipe to substantially maintain a cross-sectional shape of the pipe during operation of said trough to bend the pipe against said die and having an inner contour shaped to urge said members to mate against the exterior wall of the pipe as the pipe is impelled against said urging inner contour.
 9. A machine according to claim 8, said members of each said pair having their respective said mating surfaces diametrically opposed when mated against the pipe.
 10. A machine according to claim 9, said diametrically opposed surfaces being on opposite sides of a bending plane of the pipe.
 11. A machine according to claim 10, said bending plane being a vertical plane and said opposing pairs of members being aligned for substantially horizontal mating and releasing motion.
 12. A method for bending pipe comprising the steps of: urging the pipe against a bending die; and simultaneously girthing an exterior wall of the pipe to substantially maintain a cross-sectional shape of the pipe during bending.
 13. A method according to claim 12, said step of girthing comprising mating opposing members against opposite sides of the pipe.
 14. A method according to claim 13, said opposing members being on opposite sides of a pipe bending plane.
 15. A machine for bending pipe comprising: a beam mounted in see-saw pivotal relation on a fulcrum; first and second spaced apart cradles aligned to support the pipe, said first cradle being mounted on said beam on one side of said fulcrum and said second cradle being mounted on an actuator mounted on said beam on an opposite side of said fulcrum; and a die positioned between said cradles; said actuator initially driving said second cradle and said beam apart to pivot the pipe about said first cradle until the pipe is in contact with said die and thereafter driving said beam second cradle away from said beam to bend the pipe against said die.
 16. A machine according to claim 15, a force exerted on said second cradle by said actuator being insufficient to bend the pipe before the pipe contacts said die driving and being sufficient by application of mechanical advantage on said first cradle to bend the pipe after the pipe contacts said die.
 17. A machine according to claim 16, said mechanical advantage being leverage created by said beam and said fulcrum.
 18. A machine according to claim 15, said actuator comprising an hydraulic cylinder.
 19. A machine according to claim 15, said actuator comprising a screw drive.
 20. A machine according to claim 15 further comprising a radial control arm pivotally connected at one end to said beam and at another end to said cradle, said arm being biased to a neutral telescopic condition and responsive to expansive and compressive forces applied thereto by said second cradle to exert compressive and expansive counter-forces against said second cradle. 